# Jimism #005: Yesterday’s Logic
By 

## Article Content
One of the most dangerous things in business is an assumption that used to be correct. That's Yesterday's Logic. It happens when we keep making decisions based on rules, beliefs and operating models that made perfect sense in the world in which they were created. Except the world changed. Your logic didn't. Yesterday's Logic sounds like this: "Our customers have always wanted this." "Our competitors have always been these companies." "That's how this industry works." "People won't buy that online." "Battery economics will never make sense." "AI can't do that." Until suddenly they do. The problem is that old assumptions rarely announce that they've expired. They just quietly begin producing worse decisions. Three ways to fight Yesterday's Logic: Audit assumptions, not just results. Ask what underlying belief led to the decision.Look for statements containing "always" and "never." They're often where obsolete thinking hides.Ask what would have to be true for the opposite assumption to become correct. You may discover that it already is. Experience matters enormously. But experience becomes dangerous when it turns into certainty. The goal isn't to throw away everything we learned yesterday. It's to recognize when yesterday's lessons no longer describe tomorrow's world. Sometimes the first thing you need to update isn't the strategy. It's the mental model underneath it. jimisms.jimcarroll.com

---
Source: https://jimcarroll.com/2026/09/jimism-005-yesterdays-logic/